In a telecommunications network a call initiated by a calling entity to a called entity is routed through a number of switching nodes before it reaches its destination. An example of how a call may be routed from a calling entity to a called entity in a telecommunications network is given with reference to FIG. 1a. A calling entity CE100 sets up a call to a called entity CE105 by sending a call set up request to a switching node 101. The switching node 101 receives the call set up request and analyses the destination number comprised therein, which is typically a number associated to the user of called entity CE105. Depending on the outcome of the analysis the switching node 101 will select the most appropriate next switching node for routing the call further in the most efficient way, thereby using as few as possible switching nodes in the call path to the destination. The switching node 101 selects a switching node 102. Switching nodes 102 and 103 behave in a similar way and route the call further towards switching node 104, which is closest to the called entity CE105. Accordingly a call path is established from the calling entity CE100 to the called entity CE105 with a call path direction as depicted. In general, a call path is a sequence of switching nodes that are subsequently involved in the routing of a call between a calling entity and a called entity. A call path direction is defined to be the course on which the call is being routed or is aimed to be routed, starting at the calling entity and ending at the called entity. Switching nodes 102 and 103 are sometimes also referred to as transit switching nodes, because they function as transits between switching nodes 101 and 104. The switching node 104 then connects the incoming call to called entity CE105 and a speech connection may be opened.
Rerouting, also referred to as Pivot Routing or Redirection, is another routing mechanism that has been specified for example in ITU Telecommunication Standardization Sector (ITU-T) recommendation Q.370 (12/1999). Rerouting can be used to set up a call to a further destination, other than the called entity. The further destination for the purpose of rerouting will be referred to as the rerouting destination entity in the remainder. The switching node in the call path that decides to reroute the call may also be referred to as the invoking node. Depending on the rerouting destination entity, the invoking node may request either a succeeding node in the call path direction to the called entity to reroute the call to the rerouting destination entity, or a preceding node. Such a node should support rerouting, that is, has the capability to perform the rerouting. A switching node that has the capability to reroute a call is also referred to as a rerouting node in literature. A switching node may have the capabilities to act as either or both an invoking node and a rerouting node.
An example of rerouting is given with reference to FIG. 1b. Depicted are main switching nodes 107 to 110 that co-operate when rerouting of a call is required. A switching node 107 propagates a call towards a destination number associated to a called entity CE111, as received from a calling entity CE106. Since the switching node 107 in this example supports rerouting, i.e. has the capability to perform rerouting, if requested by an invoking node, it indicates so to the next switching node. The switching node 107 may include for example a dedicated parameter comprising a rerouting indicator in a call set up message, for example the Initial Addressing Message (IAM) as specified in the Integrated Services Digital Network (ISDN) User Part (ISUP) call control protocol.
During the call set up process the call may transit through one or more (transit) switching nodes 108, similar to the example of FIG. 1a. Any switching node 108 will pass the rerouting indicator as received from the switching node 107 transparently. The decision that rerouting has to be invoked is taken at a switching node 109 acting as the invoking node in this example. The switching node 109 also determines the rerouting destination entity RDE112. Since the call set up message indicates that rerouting can be performed by a preceding switching node in the call path direction, viz. the switching node 107, the switching node 109 requests the preceding switching node 108 in the call path direction to propagate the call back towards the switching node 107 (i.e. opposite to the call path direction to the called party CE111), indicated by the dashed arrow. The switching node 107 then reroutes the call to the rerouting destination entity RDE112. The call may transit via further transit switching nodes between the switching node 107 and the rerouting destination RDE112, not depicted. All network resources, i.e. the one or more transit switching nodes 108 between the switching node 107 and the invoking node 109 are released and can be used for new calls.
In addition to so-called network services such as rerouting, i.e. services executed by and under the control of switching nodes, there are also Intelligent Network services that are executed and controlled by an Intelligent Network (IN). According to the IN concept, service intelligence or service logic is separated from switching functions. This separation basically enables network operators to develop and deploy services and features independently of vendors, allowing more flexibility in service development, simplified rollout, reduced costs and greater autonomy. Examples of IN protocols are the Intelligent Network Application Protocol (INAP), the Advanced IN (AIN), and the Customized Applications for Mobile network Enhanced Logic (CAMEL). INAP was developed for fixed line networks and is the primary protocol used for fixed line IN outside of North America. AIN is a variant developed for North America.
CAMEL is a Global System for Mobile communications (GSM) Phase 2+ and Wideband Code Division Multiple Access (WCDMA) network feature specified in 3GPP TS 22.078. CAMEL is based on core INAP with modifications to take into account, amongst others, subscriber mobility. In particular, CAMEL enables the use of operator-specific services by a subscriber even when roaming outside the subscriber's Home Public Land Mobile Network (PLMN). A CAMEL-based Intelligent Network comprises as main entities a service switching entity for switching tasks, also referred to as SSF (Service Switching Function) or gsmSSF (GSM Service Switching Function) and a service control entity comprising the service intelligence or logic also referred to as SCF (Service Control Function) or gsmSCF (GSM Service Control Function).
Rerouting, as stated before, is a network service that is executed by and under control of switching nodes, whereas IN services are executed under the control of a service control entity and invoked for certain calls only. Because of the two levels of control that are also separate from each other, inconsistencies may occur when an IN service is invoked for a call that may be in addition subject to rerouting. For example, a call may be rerouted by a switching node to a rerouting destination entity, that according to the service logic of an IN service is on a barred list, resulting in inconsistent or undesirable service behavior. Furthermore, the service control entity may apply rerouting itself not having knowledge of rerouting capabilities of switching nodes. This may lead to unnecessary occupation of network resources and rerouting failures.